There will also be upgrade works at Drumcondra station, to include new ticket gates, and a new lift at Tara Street station.

It will result in a mix of services on the Kildare commuter line, including to Heuston and Grand Canal Dock.

David Franks, chief executive of Iarnrod Eireann, said the works will mean improved connections for new and existing commuters.

"They will be of particular benefit for those commuting between the Kildare line and the south city area served by Pearse and Grand Canal Dock, offering direct connections which are not currently available by public transport," he added.

At one time, the tunnel was used to allow direct services between Galway and Dundalk, Limerick and Drogheda and even Cork to Belfast.

It was also used for transporting west and southbound post from the mail boat docking at Dun Laoghaire.

The tunnel was built in just over two years by 1877 by the Great Southern and Western railway company, at a time of intense rivalry between privately owned operators in the capital.